1. Field of the Invention
The present invention relates to a double acting pressure intensifier or pressure booster with a pressure intensifier piston, which is automatically reversed in its limit positions.
2. Brief Description of the Prior Art
The pressure intensifier piston of known double acting pressure boosters is provided as a disk piston pressurized with the primary pressure and furnished with two thinner high pressure pistons disposed symmetrically relative to the middle plane. The disk piston together with the bore hole in which it slides forms two low pressure work volumes, which are alternatingly subjected to the low pressure power providing fluid. A directional control valve controls the low pressure oil stream and the directional control valve is actuated by pilot valves or by control switch valves. The low pressure part practically operates as a linear hydraulic motor while the two high pressure parts operate as a valve controlled pump. The disadvantage of these pressure intensifiers includes the expenditure required for the control members and the relatively large span of time required for switching the pressure intensifier piston and the pressure drop caused by the procedure.
Pressure intensifiers switching at their end positions have been constructed in order to eliminate the disadvantages of these pressure converters, where a control shell is disposed surrounding the pressure intensifier piston and controlling the feed and discharge. According to such an arrangement the control shell is shifted with stops of the pressure intensifier piston while approaching its end position and thus the driving force of the pressure intensifier piston is controlled. Since the mechanical control of the control shell despite corresponding auxiliary measures does not result in a stable switching at the end positions, a hydraulic control arrangement was constructed. In this construction the ring surfaces of two shoulders at the outer diameter of the control shell are alternatingly connected to the pressure feed or discharge side depending on the position of the pressure intensifier piston. The setting adjustment motion of the control shell is always provided against the direction of motion of the pressure intensifier piston. The cut control bores are rapidly and completely released by the opposite motion to the pressure intensifier piston, whereby the control shell is reliably moved in the other position such that a stable switching of the direction of motion of the pressure intensifier piston is assured under any condition, for example in cases where a small or a large transport flow or, respectively, pressure is present. The assured switching of the pressure intensifier piston is therefore tied to a geometrical coordination of the pressure intensifier piston to the control shell and this appears to be possible only if pressure intensifier piston and control shell contact each other or, respectively, if the pressure intensifier piston is surrounded by the control shell.
This coaxial coordination of the pressure intensifier piston and of the control shell, in particular in cases where the latter is surrounded by three additional control bushings, is disadvantageous regarding production requirements. Small deviations from a coaxial arrangement result in a clamping and sticking of the control shell in cases where the interspaces are to be kept small in order to reduce leakage losses.